Server timing out when sending larger messages

[Catscrash]

Hi,

Ich hab einen neuen VPS-Server, der mir einige Probleme mit Timeouts
gibt, die ich so noch nie hatte. Die Probleme tauchen bei manchen
Providern bei allen Mails auf, bei anderen nur bei größeren (~800k = größer)

Das sieht dann in etwa so aus:

Mar 24 18:02:08 __HOST__ postfix/smtp[27831]: Anonymous TLS connection
established to mail.XXX.org[XX.XX.XX.XX]:25: TLSv1.2 with cipher
AECDH-AES256-SHA (256/256 bits)
Mar 24 18:08:06 __HOST__ postfix/smtp[27831]: 7F4D8D486F7:
to=<xx at xx.xx>, relay=mail.XXX.org[xx.xx.xx.xx]:25, delay=19438,
delays=18916/0.03/169/353, dsn=4.4.2, status=deferred (conversation with
mail.XXX.org[xx.xx.xx.xx] timed out while sending message body)

Passiert mit gmail, t-online, etc. aber auch mit einem anderen meiner
Server, der normalerweise keinerlei Probleme macht, sodass ich da auch
mal die Gegenseite sehen kann:

Mar 24 18:02:08 root postfix/smtpd[28051]: Anonymous TLS connection
established from __HOSTNAME__[yy.yy.yy.yy]: TLSv1.2 with cipher
AECDH-AES256-SHA (256/256 bits)
Mar 24 18:02:19 root postfix/policyd-weight[12338]: decided
action=PREPEND X-policyd-weight:  NOT_IN_SBL_XBL_SPAMHAUS=-1.5
NOT_IN_SPAMCOP=-1.5 (only DNSBL check requested);
<client=__HOSTNAME__[yy.yy.yy.yy]> <helo=__HOSTNAME__>
<from=ZZZ at __HOSTNAME__> <to=xx at yy.zz>; delay: 1s
Mar 24 18:02:19 root postgrey[18205]: action=pass, reason=recipient
whitelist, client_name=__HOSTNAME__, client_address=yy.yy.yy.yy,
sender=ZZZ at __HOSTNAME__, recipient=xx at yy.org
Mar 24 18:02:19 root postfix/smtpd[28051]: 73104482C241:
client=__HOSTNAME__[yy.yyy.yyy.yy]
Mar 24 18:02:40 root postfix/cleanup[28654]: 73104482C241: message-id=<>
Mar 24 18:03:56 root postfix/smtpd[28683]: initializing the server-side
TLS engine
Mar 24 18:17:27 root postfix/smtpd[28051]: timeout after DATA (16309
bytes) from __HOSTNAME__[yy.yyy.yyy.yy]


postconf -n:

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
append_at_myorigin = yes
append_dot_mydomain = no
biff = no
broken_sasl_auth_clients = yes
config_directory = /etc/postfix
dovecot_destination_recipient_limit = 1
imscp-arpl_destination_recipient_limit = 1
inet_interfaces = all
inet_protocols = ipv4
local_destination_recipient_limit = 1
local_recipient_maps = unix:passwd.byname $alias_database
local_transport = local
mail_spool_directory = /var/mail
mailbox_command = procmail -a "$EXTENSION"
mailbox_size_limit = 0
message_size_limit = 0
mydestination = $mydomain
mydomain = __HOSTNAME__.local
myhostname = __HOSTNAME__ 
mynetworks_style = host
myorigin = $myhostname
recipient_delimiter = +
relay_domains = hash:/etc/postfix/imscp/relay_domains
smtp_bind_address = yy.yyy.yyy.yyy
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
smtp_tls_loglevel = 1
smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
smtp_tls_protocols = !SSLv2, !SSLv3
smtp_tls_security_level = may
smtpd_banner = $myhostname
smtpd_data_restrictions = reject_multi_recipient_bounce,
reject_unauth_pipelining
smtpd_helo_required = yes
smtpd_helo_restrictions = permit_mynetworks, permit_sasl_authenticated,
reject_invalid_helo_hostname, reject_non_fqdn_helo_hostname
smtpd_recipient_restrictions = reject_non_fqdn_recipient,
reject_unknown_recipient_domain, permit_mynetworks,
permit_sasl_authenticated, reject_unauth_destination,
reject_unlisted_recipient, permit
smtpd_relay_restrictions =
smtpd_sasl_auth_enable = yes 
smtpd_sasl_authenticated_header = yes
smtpd_sasl_path = smtpd
smtpd_sasl_security_options = noanonymous
smtpd_sasl_type = cyrus
smtpd_sender_restrictions = reject_non_fqdn_sender,
reject_unknown_sender_domain, permit_mynetworks, permit_sasl_authenticated
smtpd_tls_CAfile = /etc/ssl/private/ca-bundle.crt
smtpd_tls_auth_only = no
smtpd_tls_cert_file = /etc/ssl/private/xxxxxx.pem
smtpd_tls_key_file = /etc/ssl/private/xxxxxx..key
smtpd_tls_loglevel = 1
smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
smtpd_tls_protocols = !SSLv2, !SSLv3
smtpd_tls_received_header = yes
smtpd_tls_security_level = may
transport_maps = hash:/etc/postfix/imscp/transport
virtual_alias_maps = hash:/etc/postfix/imscp/aliases
virtual_gid_maps = static:8  
virtual_mailbox_base = /var/mail/virtual
virtual_mailbox_domains = hash:/etc/postfix/imscp/domains
virtual_mailbox_limit = 0
virtual_mailbox_maps = hash:/etc/postfix/imscp/mailboxes
virtual_minimum_uid = 999
virtual_transport = dovecot  
virtual_uid_maps = static:999

Eigentlich ist der VPS recht flott und reagiert schnell, ping zeiten
sind sehr gut und ich habe ansonsten noch nichts bemerkt was langsam
erscheint, aber aus irgendeinem Grund scheint das bei SMTP nicht der
Fall zu sein. Ich hab sicherheitsalber iptables geflushed, falls da
irgendwas blockendes drin ist, hat aber nichts geholfen.

Habt ihr eine Idee?

Danke!